The safety valve can prevent boilers, pressure vessels, pipes and other equipment from overpressure damage. If the fluid pressure is slightly beyond standard working pressure, namely the opening pressure, the valve will open and let partial liquid out to reduce the pressure. When it is less than standard figure, the valve will close and stop discharging to maintain sealing.

Apparently, the valve aims to protect the valve and other equipment by preventing the pressure in pipes or devices from exceeding specified limits. It is normally-closed under external force, and will automatically open if the medium pressure within equipment or pipes is higher than the specified valve, so as to discharge some medium and adjust pressure.

It can be divided into low-lift safety valve with opening height less than or equal to 0.05d0 and full-lift safety valve with opening height less than or equal to 0.25d0.

According to structure, the valve falls into hammer type, lever type, spring type and pilot-operated type. It also can be distributed into closed type and open type. The former lets discharged poisonous and corrosive medium flow through the outlet to a certain position. The latter is used to transmit air or steam. The selection of safety valve is supposed to depend on actual sealing pressure. Furthermore, spring-loaded safety valves vary on the basis of springs with different working pressure within certain PN range. So an order should give clear indication of model, name, medium, temperature as well as sealing pressure.